Mesh electrode support structure



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il ,li Ihm l www@ Sn S; A .i NM@ E R U T C m o ST 6 EMR U ms w E u ND AIl Amm N mvg n ww. QN Bm 1 rffff/a, l1lz1 'fr f f l ...ff f a f r .1 r En V/H/.` f 4 n n f 1,', I u '/f/ m ,vn l 1 ,/l. H s E M N IL w Aug. 24,1965 ,.,UmZZH/ZZZZZZZZZ%ZZZ%ZZZZZZZZZZZXZZZZZZZZZZZZZZXZZZZZJXZZZZ,.,lill JNVENTOR. ,Basil Antoniades United States Patent() 3,262,8S7 MESHELECTRBE SUEGRT STRUCTURE Basil Antonia-des, Lancaster, Pa., assigner toiRadio Corporation of America, a corporation of Delaware Filed Aug. 36,1965i, Ser. No. 52,933 3 Claims. (Ci. 313-89) This invention relates topickup or camera tubes of the type having a photoconductive material asthe photosensitive element. In particular, this invention relates to animproved photoconductive pickup tube having a novel, rigid mount lforthe decelerating mesh screen electrode.

One of the several known types of pickup tubes generally comprises anevacuated tubular envelope enclosing an electron gun and aphotoconductive target electrode. The target electrode is supported upona transparent support member, which normally is the optically cleartransparent face plate sealed to the end of the envelope and .facing theelectron gun. The target electrode includes a transparent conductivecoating, .or signal electrode, on the gun side of the transparentsupport member, and a deposit of photoconductive material on thetransparent conductive coating. vP-hotoconductive materials arematerials which change their electrical conductivity in response toincident radiations. These materials have a relatively high electricalresistance when in the dark and a relatively high electric-alconductivity when exposed to light of a selected wavelength. Closelyspaced adjacent to .the surface .of .the photoconductive material thatis exposed to the electron beam is la line mesh screen or beamdeceleratin g mesh electrode.

One of the problems that has limited the usefulness of the tubes brieflydescribed above, is the problem of microphonics. Microphonics is aphysical vibration of some portion of a tube which, because of itsmovement, produces an undesired electrical signal output or noise. -Oneof the principal electrodes in a tube of the type discussed, whichcauses microphonic action, is the iine mesh screen or decelerating meshelectrode. The mesh screen electrode is particularly troublesome whenconsidering microphonic action. The reasons for this stem from the factthat the electrode is an extremely .iine mesh, eg., 700-1000 wires perinch, and the electrode is supported `on an annular ring like memberpositioned at the periphery of the mesh screen. Because of this type ofsupport and the `fineness of the screen itself, any physical movement ofthe tube is likely to start vibrations of the mesh screen electroderelative to the photoconductive target. Because of the close spacingbetween the mesh screen electrode and the photoconduotive target,relatively large electrical noise signals are produced in Ithe output ofthe tube as a result of such motion.

The problems of microphonic action are particularly pronounced in ashutter type television camera. in this type of camera, a shutter isopened and closed mechanically to expose a particular scene. Themechanical movements necessary to open and close the shutter may, attimes, be enough to set the mesh screen electrode into vibration. .In aslow speed scanning unit, because of the use of a scan time which isrela-tively short, a constant microphonic signal becomes a relatively`large part or proportion of the total output signal and thus, is more`observable.

it is therefore an object of this invention to provide an improvedphotoconduct-ive pickup tube.

It is a further object to provide a novel photoconductive camera tubecharacterized in its rugged structure and freedom from objectionablemicrophonic action.

These and other objects are accomplished in accordance with thisinvention by providing a novel photocon- 32h25?? Patented Aug. 24, 1965ductive camera tube wherein the decelerating mesh .screen electrode isphysically supported between two metallic members each having arectangular opening or aperture in the center portion thereof. Theapertures in the metallic members are of a size slightly larger than thescanned area of the adjacent photoconductive target. By bonding themetallic members together, with the mesh screen `sandwichedtherebetween, a more rugged mesh support structure is provided and therectangular opening in each metallic member tends to dissipate theenergy of any vibrations at the corners of the openings and thus,substantially reduces the amplitude and persistance of any meshvibrations which may occur.

The invention 4will be more clearly understood by reference to theaccompanying single sheet of drawing wherein:

FIG. l is a longitudinal sectional view of a Photoconductive .type ofpickup .tube in accordance with this invention; and,

FlG. 2 is a sectional view taken along line 2 2 of FIG. l. l

Referring now to FIG. 1 in detail, there is shown a photoconductivepickup tube i0 of a type known commercially as a Vidicon and whichincludes features constituting improvements in accordance with thisinvention as will be pointed out hereinafter. The tube 10 comprises anelongated, evacuated envelope l2 having an electron gun i4 in one endthereof, and positioned substantially on the axis of .the tube. Theelectron gun ifi is provided for the punpose of producing an electronbeam and directing the beam towards a target electrode 16. The targetelectrode 16 comprises a transparent electrical conductor i8 supportedupon a transparent end or face plate Ztl of the envelope 12. On thetransparent electrical conductor 18 there is provided a photoconductivemember 22. The photoconductive member is made of a material theresistance of which decreases when exposed to radiant energy. Manyphotoconductive materials are known for many diierent spectral regionsand one material for the visible spectrum, by way of example, isantimony tri-sulfide. The transparent conductor 18 may be made of anymaterial which is electrically conductive and transparent to theradiations to which the photoconductor 22 is responsive, and a suitablematerial for the visible range is tin-oxide, for example. Thetransparent conductor 18 is connected to an electrically conductivesealing ring `24- so that a potential may be applied through the sealingring to the conductor 13 during .tube operation. In this way, thetransparent conductor .18 will function as an output electrode or signalplate.

The electron gun 14. comprises a thermionic cathode 26, a control grid2g, an apertured accelerating electrode 36, and a hollow tubular beamfocusing electrode, or G3 electrode 34.

In the conventional photoconductive pickup tube, the tubular beamfocusing electrode 34 is terminated at one end thereof, by a tine meshscreen that spans the ends of the beam focusing electrode and issupported thereby. Since the mes-h screen normally is made ofelectroformed copper, and .has at least 700 wires per inch, the meshscreen electrode is conventionally supported .by spot welding `on-to anannular ring which is substantially the same diameter as the end of thebeam focusing electrode 34. The annular ring is then `ixed to .the beamfocusing electrode 34.'

In accordance with this invention, however, a mesh screen electrode 36is sandwiched between two apertured metallic mesh support members 33 and40. The metallic member 3S has a rectangular opening 44 therein (FIG.l), and the metallic member 40 has a rectangular opening 42 therein(FIG. 2). The rectangular openings 42 and 44 may be square, as shown, ormay be similar in Y Y' shape to the scanning raster, which is producedby con-Y.

ventional scanning coils and `delection yokes (not shown) and .whichnormally basa 4 X3 aspect ratio. The rectaneecasez Y gular openings42and 44 are of asize `only slightly larger than the scanned areaof thephotoconductivetarget 16. Thus, fora conventional linchdiameter tube,Van opening of =`one-half inch has been found to be suitable.

' Trhermesh support members 3S and 4i?V are made of a a. Yrather rigidmaterialrso that they will notV be susceptible Y to any vibrations. Asan example,mesh Ysupport'm'embers made 'of 0.015 inch thicknickel-chromium alloy have vbeenV successfully used. Y Y Y As analternative to the assembly shown inFIGS. 1 and `supportrnembe'r 38 or40, and a standard' annular ring used Vas the other support member.VSuch an arrangement VVdecreases theV harmful effects of vibrations'tosomeV extent Y `*but is not preferred. The embodiment shown in FIGS. 1and 2 is Vmuch more eiective in eliminating microphonic action andtherefore is preferred. f

" VEither ofthe mesh support members 38'and .40, or both, Vmay be'coinedin such a manner so as to produce` a member that is very slightlythinner, eg., 0.09025V inch, adjacent tothe rectangular aperture Y44 or42, lthan Vthe. por- Vtionof the memberrthat is adjacent to the Vouterkperipheral h,edgel Such a structure; is believed to retard Yany mesh Yjscreen vibrations for reasons setV forth above,dandinrarddi jtion, byVabsorbing the energy ofV such vibrations Vas the Y mesh screen goesintofand out of contact with the thinned Y lor coined ,downY area orareas.

Tormanufacture the Vdecelerating mesh screen sub- Y a' assembly, themesh screenelectrode 36 is positionedV on Lthe metallic meshsupport'member 38 and, the meshV screen'36 is in turn coveredrby themetallic mesh support member 40 ,.viththeV apertures 42 and-44 inregistration.

Y YAYThe metallic mesh support membersA 33 andr() are thenY spot Weldedtogether at a plurality of areas lboth adjacent to the peripherythereofand adjacent to the apertures 42 and 44. VVThe spot weldingrxesthe mesh support memthis sub-assembly isrcompleted, the metallic'member40 may berspot'V welded to anend of an annular member l46.

- 0n the annular member 46 is an extension or lip 48 Awhich Vmay beseatedin the decelerating electrode 34 in a snap-in arrangement, orrmaybe spot'welded thereto.V A snap-in arrangement of a mesh screensub-assemblyis described in Y *the copending application of L.

Y 22;.195,9,"Serial'No. 815,193. Y

D. MillerV et'V al. liledMay Theoperation ofthe device 10is'characterized by substantial absence Vdofrharmful microphonic actioncaused by Vvibration ofthe mesh screen electrode;

' YlWith a ruggedized mesh screen assembly made in ac- 1 fr cordanceYwith this invention, it has been found thatthe i amplitudeVo'fmicrophoni'c limpulses 1inY theV tube 10 Vis4 reduced by more than50% as compared'to'conventional` Y tubes. Also,'the persistence of theseimpulses or vibra- Y f 'Y tions is reduced Vbymore' than 65%as'rcompared to conductive target electrode Yin said envelope andsubstantiallyYV normal to said axis and inthe path ,ofVV saidelectr'onbeam,VY

Y a mesh screen electrode extending parallel'to said photo-V conductivetarget electrode and closing an end of said Y Y andY dissipate YbothYthe primary and the harmonicror re- Yiiected vibrations.Y j f Y 'Y Whatis claimed is:

1. A camera tube comprsingan envelope having an y axis, an electron guninrsaid envelope andY substantiallyV onV Y said axis, for producing anelectron beam, aphotocon- V.electronV gun, Yand means for supportingsaid mesh screen Y2,V the mesh screen 3d maybe sport welded'to onlygoneY Y bers 38 and 40 together and rigidly secures themesh screen ,40

Y 36 between thermesh supportVmembersrSS and 4i). lAfter*Y ventionaltubes.'V Although the exact phenomena causing A ARTHUR GAUSS, JAMES D.KALLM,

electrode on said end of said electron gun,'saidV meansY Y yincluding apair of electrode support members having an outerperiphery.substantiallyicongruenttoY the outer pee riphery of said endof saidlelectron'glm, each of saidele'lc;V

trode support members having a different opening'there-1',

through, VeachrofV said Vopenings, including Vafplurality Vof rightangle` corners, said'meshV screen electrodeV being se- Y cured betweenand directlyto each of said supportmem-V bers adjacent Vto said corners.l Y

2. A'pickup tube comprising an envelope,jan electron i Y gun forproducing an electron beamV in said. envelope, a

photoconductiveV targetY electrodev in said envelope and Vin Vthe pathofrsaid electron'beam,.said'electron gun including a hollow tubularelectrode having an end Vspacedffrom, butadjacent to saidphotoconductivertargetgelectrode, an apertured annular memberhaving alip'portion iixedto `said end V,of said electron gun, first andsecondrrnesh screenV` supportmemberga mesh screen spot welded betweenand f w indirect contact vvith portions fof said mesh screen supportmembers,rone of said Vmesh screen support members being a Vfixed to saidannular member, 'both of saidV support members being Vdisc shaped andhavingrregistering aridcon-V gruent ,centrallyV positioned rectangularopenings theref; through, said electron beam beingadaptedto befsc'anned,f oversaid photoconductive target in a'predeterminfed` raster, land thesize Vof `said rectangular openings beingat leastas Y Ylargeassaidraster, Vsaid]'portions beingadjacent to said 1 openings'.

Y in the pathroffsaid electron beam, said electronjgun includinga hollowtubularrelectrode Vhaving anend spaced from,

but adjacent to, said photoconductive targetg-the improve# mentcomprising a subassemblysupported onsaidrend'of the tubularr electrodeand comprising aV irst ,meshV screen 'Y f support membera mesh. screenmembenandasecond Yimesh screen'support memberfsaid members being'iel Ytogether in the orderV recited, Vsaid mesh screen member directlyengaging each of said support members, said mesh screen support membersYincluding Aregistering centrally openings and having circularp'erj Ypositioned rectangular VWESTBYExaminers. Y I .v

3. Inapickup tube comprisingjan.envelope,,anlelectrori .i gunforproducing an electron beam in said envelope, andV Y fa Vphotocon'ductivetarget electrode in saidlenvelope and`

1. A CAMERA TUBE COMPRISING AN ENVELOPE HAVING AN AXIS, AN ELECTRON GUNIN SAID ENVELOPE AND SUBSTANTAILLY ON SAID AXIS, FOR PRODUCING ANELECTRON BEAM, A PHOTOCONDUCTIVE TARGET ELECTRODE IN SAID ENVELOPE SAIDSUBSTANTIALLY NORMAL TO SAID AXIS AND IN THE PATH OF SAID ELECTRON BEAM,A MESH SCREEN ELECTRODE EXTENDING PARALLEL TO SAID PHOTOCONDUCTIVETARGET ELECTRODE AND CLOSING AN END OF SAID ELECTRON GUN, AND MEANS FORSUPPORTING SAID MESH SCREEN ELECTRODE ON SAID END OF SAID ELECTRON GUN,SAID MEANS INCLUDING A PAIR OF ELECTRODE SUPPORT MEMBERS HAVING AN OUTERPERIPHERY SUBSTANTIALLY CONGRUENT TO THE OUTER PERIPHERY OF SAID END OFSAID ELECTRON GUN, EACH OF SAID ELECTRODE SUPPORT MEMBERS HAVING ADIFFERENT OPENING THERETHROUGH, EACH OF SAID OPENINGS INCLUDING APLURLAITY OF RIGHT ANGLE CORNERS, SAID MESH SCREEN ELECTRODE BEINGSECURED BETWEEN AND DIRECTLY TO EACH OF SAID SUPPORT MEMBERS ADJACENT TOSAID CORNERS.